I was wondering if you knew what would happen if Boris were to stand as an MP in the next election. Would he have to resign as mayor and if so how would his successor be decided?

I already knew the answer to the second part of the question. If Mayor Johnson steps down at any point between four-yearly mayoral elections his statutory deputy, presently Richard Barnes AM, would not take the helm. Instead a by-election would be held. We'd have as good as a full-on London mayoral election earlier than expected, with each party having to find a candidate - imagine the fun that would be - and the tax-payer finding, I'm told, between four and five million quid to pay for it.

That might be another reason for Boris to resist forsaking City Hall for Westminster at any point before the 2012 mayoral election - it wouldn't look good for a politician dedicated to keeping taxes as low as possible to effectively relieve the public purse of a tidy wedge in order to pursue his personal ambitions.

But what of the rest of my Leytonian reader's inquiry? I'm intrigued by thought of Boris seeking to become an MP not after David Cameron has moved into Number 10, as has been speculated about widely, but before - in other words some time in the next couple of months. The scenario seems unlikely, even for so uninhibited a politician as Boris (though I have invited his office to rule the possibility out. Watch this space). And so to the first part of the question. If Boris - or any future London Mayor - were to stand as an MP, would he have to resign as Mayor?

The answer is no. What's more, he wouldn't have to resign as Mayor even if he won the seat. The GLA tells me there is no legal or constitutional impediment to Boris subsequently becoming Mayor Johnson MP (Update, 12:20 As opposed to the reverse: ee DBIV comment below). There would be a financial penalty: a London mayor who becomes a member of either House of Parliament (or the European Parliament) loses two-thirds of his mayoral salary (see para 2.1). But given that the bulk of Boris's steady income comes from the Daily Telegraph and (presumably) he'd receive an MP's salary too, he'd probably scrape by.

And here's another thought. If a Mayor can simultaneously be an MP, is there anything to prevent him or her also being a mayor and a minister? A mayor and a prime minister, even? You may laugh at the idea. I may laugh at it too. But Boris is the complete cake-and-eat-it man. I wonder if he's laughing too.